Electrical submersible pumps (ESP) are often employed to pump well fluid from wells. A typical ESP includes a rotary pump driven by an electrical motor. Normally, the ESP is suspended in the well on a string of production tubing. A seal section, usually located between the motor and the pump, has a movable element to reduce a pressure differential between the well fluid exterior of the motor and motor lubricant contained in the motor. The pump may be a centrifugal pump having a plurality of stages, each stage having an impeller and a diffuser.
Some wells produce gas along with liquid. Gas flowing into the pump can accumulate in pockets. The gas pockets can reach a size causing the pump to gas lock. When gas locked, the pump ceases to pump liquid. Unless remedial action is taken soon, the gas lock can cause excessive heat and damage to the ESP.
Gas separators of various types may be employed to separate the gas from the liquid prior to reaching the pump. However, some gas may still reach the pump, causing gas pockets to accumulate. Various designs to the impellers have been proposed to inhibit the formation of gas pockets. For example, U.S. Pat. No. 6,676,366 discloses split vanes having an inner vane member offset from an outer vane member.